Synthesis and photoinduced electron transfer of phthalocyanine- perylenebisimide pentameric arrays

(Figure Presented) Zinc phthalocyanine-perylenebisimide pentameric arrays, ZnPc(PDI)₄ 1 and 2, have been synthesized. ZnPc(PDI)₄ 1 has no substituents in the PDI bay positions, while ZnPc(PDI)₄ 2 presents four phenoxy groups in the bay positions of each perylene. In both cases, the PDI moieties are directly connected to the ZnPc. As a consequence of aggregation, photoexcitation of 1 affords the intermolecular exciplex rather than the charge-separated state. In contrast to 1, photoexcitation of 2, which contains sterically demanding substituents in the PDI moieties, affords the charge-separated (CS) state, which was clearly detected by its transient absorption spectrum in femtosecond laser flash photolysis measurements. The CS lifetime was determined to be 26 ps. The addition of Mg(ClO₄) ₂ to a benzonitrile solution of 2 and the photoexcitation affords the long-lived CS state with the lifetime of 480 μs, whereas no such long-lived CS state was formed in the case of 1 under such conditions. The remarkable elongation of the CS lifetime results from the strong binding of Mg²⁺ to the PDI^•- moiety in the CS state.